Actuators adapted for the sliding means to move and guide linearly any object are recently availed in extensively increased fields. Modern actuators are needed to be less in weight and height in transverse section, and more compact in construction. The actuators of the sorts as stated earlier have been used in, for example assembling machines, measurement instruments, various machines, industrial robots, semiconductor manufacturing equipments, and so on.
An example of the prior actuators is disclosed in, for example the Japanese Laid-Open Patent Application No. H08-126 247, which is composed of a base and a slider movable with respect to the base. With the prior actuator, the base and the slider are both made of extrusions of light-metal alloys. The base has lengthwise guide rails while the slider also has guide rails same in transverse section with the rail on the base. All the guide rails on the base and slider are formed by grinding or plastic working. The guide rails along their preselected locations are subjected to heat treating or hardening to prepare raceway grooves to allow rolling elements running through there. The guide rails are fastened to their respective base and the slider and further raceway grooves are worked with grinding operation to have gothic-arched contour in transverse section.
Further for example in the Japanese Laid-Open Patent Application No. H11-159 529 there is disclosed a linear motion guide unit in which a guide rail is made of a composite of a rail member with a guide rail support. With the composite, the rail member is first assembled with the guide rail support in a way sidewise flanges of the rail member fit into mating grooves cut in advance. The assembly of the rail member and the guide rail support is pulled or drawn to apply a load to the rail member.
A prior linear motion guide unit is disclosed in, for example the Japanese Laid-Open Patent Application No. H06-272 713 in which a track construction is made up of a base and a rail member that fits into grooves cut in the base while a moving construction is made up of a slider and a guide member that fits into grooves cut in the slider. With the linear motion guide unit constructed as stated earlier, a contact angle θ between a rolling element and a raceway groove made on the track construction is set in a range of from 30° to 40° wherein θ refers to an angle formed by a horizontal line passing through a center of the rolling element and a line extending from a contact point between the raceway groove and the rolling element to a center of the rolling element.
The prior actuator as recited earlier, nevertheless, is generally bulky in construction. The recent actuator in which the slider is driven unidirectionally is needed adding increasingly less weight and taking up less space and less production cost. Especially, there is a need of advanced actuators which are compact in construction, more particularly, less height in transverse section, more simplified in construction and less expensive in production.